Polymerase chain reaction (PCR) is one of the popular nucleic acid amplification techniques in molecular diagnostics. Almost all commercial PCR systems adopt a thermocycler to perform heating and cooling and so as to have the deoxyribonucleic acid (DNA) to experience three typical temperature cycles; denaturation at 95° C., annealing at 45-65° C. and extension at 72° C. In each thermal cycle, a metal block is applied to transfer the heat to the reaction tube by thermal conduction, and a predetermined time is kept for reaction. However, such indirect heating method for PCR would spend lots of time in heating or cooling the metal block. Therefore, it is the reason why the reaction time of the PCR cycles is usually long and the systems for PCR always occupy too much space.
In addition, various developments on PCR chips with micro channels have been announced. In particular, the laboratory on a chip (LOC) is one of those devotions targeted to integrate micro channels and micro structures into the LOC capable of performing various reactions on a single chip, including various specimens' management, reactions, analysis or detections. Expectable advantages of the LOC are size miniaturization, rapid temperature control, reduction in the number of the required samples, cost-down and so on. However, though many researches demonstrate the merits of the PCR and LOC, yet a real mature commercial product of the PCR chip is yet to come. One of the reasons for such a situation in PCR chips is the low repeatability in the related researches. Furthermore, the requirement of a hydraulic driving system also limits the application of the PCR chips. Hence, it can be foreseen that the appearance of a commercial PCR chip shall need more efforts.
Currently, one of the temperature setting methods and structural designs for the PCR reactions is to place a test tube containing a mixture solution and DNA specimens into a sealed casing and then apply a heating device to heat the bottom portion of the test tube to the denaturation temperature so as to produce a temperature gradient thereof for further inducing a convection flow thereinside. Thereby, the PCR reaction can be maintained in a looping manner as the convection persists. In particular, the method and the apparatus for controlling temperature of the PCR are featured in simply structuring, low cost, requiring less time for changing temperatures, and being suitable to a single heat source environment.
Furthermore, a special reaction test tube furnished to a DNA amplification reaction includes mainly a plastic capillary tube wrapped with a metallic ring at the bottom. While this tube is arranged on a heating block with the metal ring contacting the block, the heat would be transferred to the liquid within the tube, such that the temperature of the liquid can be controlled around 95° C. In particular, the upper cap of the capillary tube is removable and thus can be applied by another temperature control at about 50° C., such that a temperature gradient between the bottom and the head of the tube can be controlled. Thereby, the PCR reagent inside the tube would be amplified time after time by the convective temperature cycling. Such a concept of heating the PCR reagent within the test tube which has a conductive ring under a single heat source is the topic of this current disclosure concerns.